Permissible Exposure Limits (PEL's) are set by OSHA to protect workers from exposure to airborne hazards. PEL's set regulatory list on the concentration of a substance in the air. They are based on an 8 hour time weight average exposure. This determines the level of allowable exposure over an 8 hour time period.
Each has specific PEL limits that have been set for substances that a re unique to their operation. OSHA have set some 500 PELs for various chemicals and compounds across industries. Many of them are contained in the air contamination standards. PELs have also been established for exposure to mineral dust, including silica, graphite, coal dust and inert or nuisance dusts.
Twenty four states have adopted their own standards and enforcement policies. Most of these standards and enforcement are identical to Federal OSHA regulations.
The control of a specific airborne hazard depends on the nature of the hazard and the process and possibility that workers on the job will be exposed. If possible, airborne hazards should be engineered out of the worksite. If it is not possible to eliminate or reduce the hazard, you should use appropriate administrative controls should be used. Personal protective equipment should be used as a last resort.